This invention relates to a disc cartridge and a molding die therefor, and more particularly to a disc cartridge having a disc-like medium such as an optical disc, a magneto-optical disc or the like rotatably received therein and a molding die therefor.
In general, an information medium or a disc-like medium such as, for example, a magnetic disc, an optical disc, a magneto-optical disc or the like is used in the form of a disc cartridge while being received in a casing. Conventional casings for such a disc cartridge include a casing made of one kind of transparent or non-transparent resin and a casing integrally made of both transparent resin and non-transparent resin. Such a transparent disc cartridge is disclosed in Japanese Patent Application Laid-Open Publication No. 325494/1993 and Japanese Utility Model Application Laid-Open Publication No. 52064/1994 and such a non-transparent disc cartridge is conventionally used for a micro floppy disc (MFD). The assignee proposed a disc cartridge integrally formed of both non-transparent resin and transparent resin, as disclosed in Japanese Utility Model Application No. 17002/1994 and Japanese Patent Application No. 337509/1994.
Of the above-described conventional casings for the disc cartridge, the casing made of one kind of non-transparent resin or transparent or semitransparent resin is monotonous in design. This is remarkable particularly when it is made of non-transparent resin. Thus, it is difficult for a user to distinguish between non-transparent disc cartridges manufactured by different manufacturers. Also, the conventional casing made of transparent resin causes an internal structure of the disc cartridge to be observed from outside, therefore, it is required to design the disc cartridge while taking a serious view of an appearance thereof. Unfortunately, this renders manufacturing of the cartridge highly troublesome and increases a manufacturing cost thereof.
The casing integrally made of both non-transparent resin and transparent resin causes a joining surface between the non-transparent resin and the transparent resin to be disadvantageously reduced in thickness because the casing generally has a thickness as small as about 1 mm. In order to provide joining strength of a sufficient level, it is required to carry out charging of two kinds of resins prior to solidification of the resins. This requires to increase both a resin temperature and a die temperature to an increase level, leading to a deterioration in workability and a failure in molding called burns.
Also, a conventional molding die for forming conventional non-transparent resin and transparent resin into a casing is so constructed that a slide mold is arranged in a movable part of the molding die in a manner to be closely contacted with a surface of the die opposite thereto, to thereby prevent the non-transparent resin from mixedly entering a portion of the casing made of the transparent resin. The non-transparent resin is first charged in the die thus constructed, resulting in a peripheral body of a casing being formed. Then, the slide mold is retreated to form a space in the die, which is charged with the transparent resin to form a transparent window. In a conventional tape cassette, a casing is often constructed in such a manner that non-transparent resin and transparent or semitransparent resin are integrally molded into two-layer structure having a non-transparent resin layer and a transparent or semitransparent resin layer laminated on each other in a direction of thickness of the casing. In the tape cassette thus constructed, the casing has a thickness of about 1.8 mm and a sheet material of PET is interposed between a tape-like medium received therein and an inner surface of the casing, so that the casing exhibits joining strength of an enough level even if it is not formed into the two-layer structure and a joining surface is provided only in the direction of thickness of the casing. Also, the sheet effectively prevents any bur possibly formed on the casing from adversely affecting the tape-like medium. Whereas, in the conventional disc cartridge, the transparent window of the casing is generally arranged so as to be opposite to a disc-like medium and a boundary between the slide mold and the movable part causes a bur to be formed on the transparent window of the casing. Unfortunately, the bur contacts with the disc-like medium to damage a recording and reproducing surface of the medium due to lack of any sheet therebetween.